Microtubule (MT)-binding protein that plays a role in the formation and maintenance of the spindle poles and the alignement and the segregation of chromosomes during mitotic cell division . Functions to tether the minus ends of MTs at the spindle poles, which is critical for the establishment and maintenance of the spindle poles . Plays a role in the establishment of the mitotic spindle orientation during metaphase and elongation during anaphase in a dynein-dynactin-dependent manner . In metaphase, part of a ternary complex composed of GPSM2 and G(i) alpha proteins, that regulates the recruitment and anchorage of the dynein-dynactin complex in the mitotic cell cortex regions situated above the two spindle poles, and hence regulates the correct oritentation of the mitotic spindle . During anaphase, mediates the recruitment and accumulation of the dynein-dynactin complex at the cell membrane of the polar cortical region through direct association with phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), and hence participates in the regulation of the spindle elongation and chromosome segregation . Binds also to other polyanionic phosphoinositides, such as phosphatidylinositol 3-phosphate (PIP), lysophosphatidic acid (LPA) and phosphatidylinositol triphosphate (PIP3), in vitro . Also required for proper orientation of the mitotic spindle during asymmetric cell divisions . Plays a role in mitotic MT aster assembly . Involved in anastral spindle assembly . Positively regulates TNKS protein localization to spindle poles in mitosis . Highly abundant component of the nuclear matrix where it may serve a non-mitotic structural role, occupies the majority of the nuclear volume . Required for epidermal differentiation and hair follicle morphogenesis .

Cellular Localization

Nucleus Nucleus, nucleoplasm Nucleus matrix Chromosome Cytoplasm, cytoskeleton Cytoplasm, cytoskeleton, microtubule organizing center, centrosome Cytoplasm, cytoskeleton, spindle pole Cytoplasm, cell cortex Cell membrane. Mitotic cell cycle-dependent shuttling protein that relocalizes from the interphase nucleus to the spindle poles and cell cortex . In interphase, resides in the nuclear matrix . In prophase, restricted to the interchromatin or condensed chromosome space . In prometaphase, after nuclear envelope disassembly, forms aggregates both in the spindle midzone and at duplicated centrosomes and astral microtubules (MTs) of the bipolar spindle apparatus . Translocates from the spindle midzone towards the spindle poles along spindle fibers in a MT- and dynein-dynactin-dependent manner until the anaphase onset . In metaphase, recruited to the polar cortical region in a GPSM2- and GNAI1-dependent manner . Excluded from the metaphase equatorial cortical region in a RanGTP-dependent manner . Phosphorylation on Thr-2055 by CDK1 results in its localization at spindle poles in metaphase, but not at the cell cortex . In anaphase, recruited and anchored at the cell membrane of the polar cortical region in a EPB41-, EPB41L2-, phosphatidylinositol-dependent and GPSM2- and G(i) alpha proteins-independent manner . Excluded from the anaphase equatorial region of the cell cortex in a RACGAP1- and KIF23-dependent and RanGTP-independent manner . Associated with astral MTs emanating from the spindle poles during anaphase . Nonphosphorylated Thr-2055 localizes at the cell cortex, weakly during metaphase and more prominently during anaphase in a phosphatase PPP2CA-dependent manner . As mitosis progresses it reassociates with telophase chromosomes very early during nuclear reformation, before substantial accumulation of lamins on chromosomal surfaces is evident . Localizes to the tips of cortical MTs in prometaphase . Localizes along MTs and specifically to both MT plus and minus ends . Accumulates also at MT tips near the cell periphery . Colocalizes with GPSM2 at mitotic spindle poles during mitosis . Colocalizes with SPAG5 at mitotic spindle at prometaphase and at mitotic spindle poles at metaphase and anaphase . Colocalizes with ABRO1 at mitotic spindle poles . Colocalized with TNKS from prophase through to anaphase in mitosis . Colocalizes with tubulin alpha . CCSAP is essential for its centrosomal localization . Isoform 3: Cytoplasm, cytosol Cytoplasm, cytoskeleton, microtubule organizing center, centrosome Cytoplasm, cytoskeleton, spindle pole. During interphase, mainly clustered at the centrosomal region in the cytosol. After entry into mitosis, detected at mitotic spindle poles. Isoform 4: Cytoplasm, cytosol Cytoplasm, cytoskeleton, microtubule organizing center, centrosome Cytoplasm, cytoskeleton, spindle pole. During interphase, mainly clustered at the centrosomal region in the cytosol. After entry into mitosis, detected at mitotic spindle poles.